1. Field of the Invention
This invention relates to apparatus for measuring properties or electrical characteristics in an electrical circuit and more particularly to an apparatus for operating, in a novel way, an electronic counter connected to a Geiger-Mueller (GM) tube for use in detecting ionizing radiation.
2. Description of the Prior Art
Various methods are used to detect ionizing radiation. One common method employs the use of a Geiger-Mueller tube, wherein electrical pulses are produced at a rate determined by the amount of radiation present. The output from a Geiger-Mueller tube is a train of pulses that occur randomly in time characterized by an average pulse-repetition rate that is nearly proportional to the amount of ionizing radiation present within the tube at low radiation levels. Geiger-Mueller tubes are further characterized by a dead time following each pulse that they produce, during which interval they cannot respond to radiation. This dead time makes the response of the Geiger-Mueller tube non-linear at increased radiation levels, as determined through the use of the well-known dead-time equation described and discussed in detail further herein. Because the typical Geiger-Muller tube has a dead time of perhaps 100 .mu.s, the dead-time correction at 1000 counts/second is already 10%.
Non-linear meter scales and various complex circuits are known to have been used to compensate for dead-time effects, but they are not very accurate nor helpful because the dead time varies from one tube to another and sometimes as a function of radiation level. Furthermore, dead time varies for a given tube over its operating lifetime, varies over changing temperatures and varies due to other physical factors. To perform with good accuracy, frequent recalibrations of the prior-art devices and their circuitry are necessary. The use of the tube itself to control the system dead time does not provide a very reliable, stable or predictable way to provide accurate measurements at high radiation levels.